The present invention relates to a method and apparatus for refining fiberous material in a disc refiner and more particularly, to a method and apparatus for withdrawing steam developed during refining of fiberous material.
Disc refiners for refining of fiberous material, such as cellulose pulp, generally comprise two rotating refining discs which are supported for counter-rotation with respect to one another in a grinding or refining housing. The fiberous material to be refined is passed into the space between the two discs and is refined as it passes radially outward through the refining space between the two discs. Generally, the fiberous material is supplied in the form of chips through appropriate openings located close to the center of one of the refining discs. Generally, these chips especially in the refining of cellulose pulp, include water as the chips are usually steamed with hot water and/or steam before being introduced into the space between the two counter rotating discs. Further, water may be supplied in connection with the refining.
From this water, great amounts of steam are generated as energy is added during the refining operation on the fiberous material. This steam passes out of the refining space together with the refined material as well flowing rearward to a location where the chips are fed. The steam flowing outward together with the fiberous material through the refining space assumes a very high speed, often on the order of 150 to 1,000 meters per second, which as can be appreciated, disturbingly affects the material flow. Further, the steam may flow out in a jerky manner and thereby affect the stability of the grinding or refining gap, and simultaneously render the material flow through the gap nonuniform. This has a negative affect on the pulp quality.
Prior efforts to alleviate the problems associated with the generation of steam between the refining discs have involved withdrawing of steam from the central space between the refining discs. For example, Canadian Pat. No. 974,958, issued Sept. 23, 1975, for "Apparatus for Treatment of Cellulose Containing Material" discloses an apparatus and method in which steam generated during refining is withdrawn and discharged into the housing surrounding the refining discs through central openings close to the axis of rotation of the refining disc. That is, steam is withdrawn through openings arranged radially inward of the feed opening for the cellulose chips being introduced between the refining discs. While such arrangements have helped to relieve some of the problems associated with the generated steam, they have not been totally satisfactory, especially with respect to maintaining the stability of the refining gap and to assuring a uniform flow of material therethrough.